Air filtering device

ABSTRACT

A device for filtering air comprising a base, a fan functionally attached to the base, an air filter releasably attached to the base, and a substantially air impermeable outer sleeve is provided.

FIELD OF THE INVENTION

The present invention is directed to an air filtering device thatfilters dust and particulates from an incoming air stream to reduceparticulates in the filtered airstream.

BACKGROUND OF THE INVENTION

Air includes many pollutants such as odors (e.g. cigarette smoke), VOCs,microbials (e.g. bacteria, viruses, mold), particulates (e.g. dust),that have a pernicious effect when inhaled or otherwise contacted byhuman beings. Particulates alone comprise dead skin, pet dander, dustmite feces, and other microscopic (less than 5 microns in size)particulates which may elicit a human immune response.

There are several air filtering devices known in the art that areintended to remove particulates from the air. Often times, such airfiltering devices are large/bulky or utilize rigid outer housings.Attempts have been made to reduce parts and/or decrease size forconvenience, cost, and/or transportability advantages. One such deviceis described in US 2009/0038480, assigned to Hamilton Beach Brands, Inc.(“HB”). The HB device is an air purifier having an impeller housedwithin a base and having a foldable air filter bag that is removablymountable to the base. The impeller urges air through the air filter bagto remove particles from the air. In some embodiments, the HB deviceincludes a readily air pervious or permeable outer cover that is slippedover a frame surrounding the air filter. The outer cover is said toprovide an aesthetically pleasing appearance to the air purifier andprovides support to the air.

One drawback with previous air filtering devices may be the low exitvelocity of air exiting the device which affects filtering performance.Air filtering devices that achieve a sufficient exit velocity forfiltering desired particulate levels may require a higher powered fanwhich could make the device noisy or require a rigid device housing thatadds to the large size and cost of the device.

Accordingly, there continues to be a need for an improved air filteringdevice and method of filtering air which cost-effectively removesparticulates from the air and includes consumer-friendly features suchas transportability and consumer acceptable noise levels.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, there is provided an airfiltering device comprising a base having an air inlet and an airoutlet; a fan functionally attached to said base, wherein said fan movesabout 50 to about 150 CFM of air through said air outlet, with a soundpower level less than 45 dBA with about 4 to about 25 Pa of pressuredrop within the entire device, when said fan is activated; an air filterin air flow communication with said air outlet; a substantially airimpermeable outer sleeve comprising a first open end, a second open end,and an air flow path there between, wherein said outer sleeve is in airflow communication with said air outlet and is releasably attached tosaid base at said first open end, and wherein said outer sleeve envelopssaid air filter around its longitudinal axis; wherein the exit velocityof a volume of air exiting said second open end of said outer sleeve isabout 0.5 m/s to about 3.0 m/s when said device is activated.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with the claims particularly pointingout and distinctly claiming the invention, it is believed that thepresent invention will be better understood from the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows one embodiment of an air filtering the device in accordancewith the present invention;

FIG. 2 shows a cross-sectional view of the air filtering device in FIG.1;

FIG. 3 shows an exploded view of the air filtering device in FIG. 1;

FIG. 4 shows the cross-sectional view of the device in FIG. 2, showingonly the base of the device (i.e. device with the outer sleeve, airfilter, and related parts removed);

FIG. 5 is an exploded view of the base in FIG. 4;

FIG. 6 shows one embodiment of an air filter bag in accordance with thepresent invention;

FIG. 7A shows a cut-away section of the outer sleeve, taken along lineLA in FIGS. 1 and 2; FIG. 7B shows another embodiment of an outer sleevein accordance with the present invention;

FIG. 8 is a graph showing the particle reduction over time using an airfiltering device in accordance with the present invention;

FIG. 9 is a graph showing the static pressure and air flow rates of anair filtering device, in accordance with the present invention, and thepressure drops within the device associated with having varying spatialgaps between the air filter and outer sleeve.

FIG. 10 is a graph showing the static pressure and air flow rates of afan only, a device with fan and air filter only, and an entire airfiltering device, in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-3, an exemplary embodiment of a device 10 forfiltering air is shown. The device 10 may include a base 20, a fan 40functionally attached to the base, an air filter 50 releasably attachedto the base, and a substantially air impermeable outer sleeve 80. Thedevice 10 may be powered by replaceable or rechargeable batteries, an ACoutlet (directly AC driven or an adequate AC to DC power supply), a carDC power source, a solar cell, or the like.

As input air having particulates or other contaminants, which may rangein size from about 0.1 microns to about 30 microns, enters the device10, the input air is filtered through the air filter 50, thus reducingparticulates in the output air.

The device 10 may be sized such that it can be used on a table top or ina living space such as a room having about 22 m³ to about 75 m³ ofspace. The device 10 may have a smaller footprint than its uprightheight along the longitudinal axis LA to be suitable for small spaces.For example, when in its upright position, the device may be about 20 cmto about 30 cm wide, about 20 cm to about 30 cm deep, and about 45 cm toabout 75 cm tall along the longitudinal axis LA. The height of thedevice 10 may be reduced during storage where collapsible parts areused.

The device 10 may be characterized by air flow, air filter properties,and device configuration (e.g. housing, grill covers, air filter, andouter sleeve configuration). Such aspects lead to a pressure drop withinthe device 10. In one embodiment, the device 10 may result in a totalpressure drop of about 15 Pa to about 25 Pa, or about 8 Pa to about 20Pa. Other embodiments may have higher or lower pressure drops leading tohigher or lower air flow requirements for the fan 40 in order to lead tothe same air flow of the device 10.

Each of the parts that may be included in the device 10 of the presentinvention is described in more detail below.

Device Parts Base and Fan

Referring to FIGS. 4-5, the device 10 of the present invention mayinclude a base 20 constructed of any known material to stabilize amotorized fan 40. The base 20 may include a fan housing 30 and legs 32supporting the fan housing and raising the fan housing from a supportingsurface to facilitate air flow into an air inlet 22 when the air inletis located an on underside of the base. The base 20, with legs 32, maybe about 5 cm to about 10 cm tall and about 20 cm to about 30 cm indiameter to reduce part weight. The base 20 has an air inlet 22 on afirst side 23 of the base and an air outlet 24 on a second side 25 ofthe base. In some embodiments, the base 20 may include grill covers 26a, 26 b corresponding to the air inlet 22 and air outlet 24, and,optionally, a fan pre-filter 42 and fan cover 44 for filtering largeparticles (e.g. hair) to help keep the fan clean.

The base 20 may have a tapered shroud 34 with a first step 36 to enableattachment of an air filter 50 and a second step 38 for attachment of anouter sleeve 80. The second step 38 may be lower on the shroud 34 of thebase 20, circumferencing the first step 36. The shroud 34 may have adiameter at the top of about 16 cm to about 25 cm, expanding downward toabout 20 cm to about 30 cm.

A fan 40 is functionally attached to the base 20 such that it assistswith drawing a volume of input air into the air inlet 22 of the base andout through the air outlet 24, pushing the volume of air through an airflow path 90 defined by the outer sleeve 80 and through the air filter50, also located in the air flow path 90. The fan 40 may be mountedinside the base 20 between the first side 23 and the second side 25 ofthe base 20. In some embodiments, the fan 40 can be placed downstream ofan air filter 50 such that a volume of air is pulled through an airfilter (vs. pushed through the air filter) and the air filter cleans theair before passing over the fan 40. “Downstream”, as used herein, meansa position in an airflow path that is later in time from a referencedposition, when measuring air flow through an air filtering device.

The fan 40 may include a fan blade and motor. The rotating fan blade maybe at least about 5 cm from the surface upon which the device 10 reststo avoid a high pressure drop in urging air into the air flow path 90and also to minimize drawing in undesirable quantities of debris (e.g.dirt/hair). The fan 40 may be activated or powered by a power sourceproviding less than about 25 Watts, or less than about 15 Watts, or lessthan about 8 Watts, or less than about 6 Watts of power to the fan.

The fan 40 may be set at a predetermined speed to provide a desired airflow rate or may be set by a control having user-selected speeds. Thefan 40, when activated without the air filter 50 or outer sleeve 80, mayprovide from about 70 to about 150 cubic feet per minute (“CFM”), orabout 85 to about 130 CFM, or about 100 to about 120 CFM, of air.

In one embodiment, an axial fan is mounted in the base 20. Where anaxial fan is used, the desired axial fan blade (also called impeller)diameter can be measured from tip to tip at outer most point of theblade and may have a diameter of about 10 cm to about 25 cm, or about 15cm to about 25 cm, or about 17 cm to about 20 cm, and is combined withan AC or DC motor, fan housing 30, and fan speed that delivers, withoutthe air filter 50 or outer sleeve 80, about 70 to about 150 CFM, orabout 85 to about 130 CFM, or about 100 to about 120 CFM, of air.Suitable axial fans include Silverstone S1803212HN available from ConradElectronics, Orion OD180APL-12LTB available from Allied Electronics, andEBM Pabst 6212 NM available from RS Components Intl. Axial fans may besignificantly quieter than centrifugal fans typically used in airfiltering devices.

Air Filter

Referring again to FIGS. 1-3, the air filter 50 of the present inventionlongitudinally extends from the base 20 and is in air flow communicationwith the air outlet 24 of the base 20. The air filter 50 may include atleast one attachment member 52 which releasably attaches the air filter50 to the base 20. The attachment member 52 may be in the form of clips,elastic bands, gripping materials, hook and loop fasteners, and thelike. One fastening approach is to provide a tab that engages amechanical switch that is electrically connected to the fan 40 to powerit on when the air filter 50 is properly engaged.

The air filter 50 may have an air flow surface area of about 0.1 m² toabout 1 m² (about 1.08 ft² to about 10.76 ft²), or about 0.1 m² to about0.6 m² (about 1.08. ft² to about 6.46 ft²), or about 0.15 m² to about0.5 m² (about 1.61 ft² to about 5.38 ft²), or about 0.2 m² to about 0.4m² (about 2.15 ft² to about 4.31 ft²). The air flow surface area, asused herein, is the permeable area from which air flows through the airfilter 50. This air flow surface area is measured by laying the airfilter 50 out flat on a single plane without any folds or pleats andthen measuring the total surface area. The measured air flow surfacearea of the air filter 50 may not include any areas where a physical orchemical barrier (e.g. a structure or coating on an edge of the filter)prevents air flow through that part of the air filter. Using an airfilter with more air flow surface area may be desirable as it enables alower face velocity of air through the filter 50 which lowers thepressure drop. This enables a higher air flow rate (i.e. CFM) from thefan 40 for a given amount of power. Higher air flow surface area alsoenables a quieter device since less power is needed from the fan 40.

The air filter 50 of the present invention may have an average facevelocity of about 6 fpm to about 60 fpm (about 1.83 m/min to about 18.29m/min), or about 25 fpm to about 50 fpm (about 7.62 m/min to about 15.24m/min), or about 25 to about 40 fpm (about 7.62 m/min to about 12.19m/min) In one embodiment, the air filter face velocity is about 36 fpm(about 10.97 m/min). Air filter face velocity is the velocity of air asit exits the outer face of the air filter. The air filter's outer faceis downstream of the air filter's inner face such that air flows fromthe inner face to the outer face of the air filter 50. In configurationswhere air is routed directly from the fan to the air filter (i.e. airdoes not escape between the fan and an entrance point to air filter), asin the present invention, air filter face velocity is calculated:

${{Filter}\mspace{14mu} {Face}\mspace{14mu} {Velocity}} = \frac{{Volumetric}\mspace{14mu} {Flow}\mspace{14mu} {rate}\mspace{14mu} ({CFM})\mspace{14mu} {through}\mspace{14mu} {the}\mspace{14mu} {air}\mspace{14mu} {inlet}\mspace{14mu} {of}\mspace{14mu} {fan}}{{Airflow}\mspace{14mu} {surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {air}\mspace{14mu} {filter}\mspace{14mu} ( {ft}^{2} )}$

The air filter 50 of the present invention may be formed from a singlefibrous layer or multiple layers. The air filter 50 may comprise anon-woven. “Non-woven”, as used herein and as defined by EDANA (EuropeanDisposables and Non-woven Association) means a sheet of fibers,continuous filaments, or chopped yarn of any nature or origin, that havebeen formed into a web by means, and bonded together by any means, withthe exception of weaving or knitting. The non-woven may be composed ofsynthetic fibers or filaments or natural fibers or fibers post-consumerrecycled material such as polyolefins (e.g., polyethylene andpolypropylene), polyesters, polyamides, synthetic cellulosics (e.g.,RAYON®), and blends thereof. Also useful are natural fibers, such ascotton or blends thereof. Non-limiting examples of how the non-woven canbe formed include meltblowing, carded spunlace, carded resin bonding,needle punch, wet laid, air laid, spunbond, and combinations thereof. Anon-woven air filter may have a basis weight of about 20 to about 120gsm, where the basis weight of the non-woven or filter media is measuredaccording to the following method that follows a modified EDANA 40.390(February 1996) method.

-   -   1. Cut at least 3 pieces of the non-woven or filter media to        specific known dimensions, preferably using a pre-cut metal die        and die press. Each test piece typically has an area of at least        0.01 m².    -   2. Use a balance to determine the mass of each test piece in        grams; calculate basis weight (mass per unit area), in grams per        square meter (“gsm”) using:

${{Basis}\mspace{14mu} {Weight}} = \frac{{Mass}\mspace{14mu} {of}\mspace{14mu} {Test}\mspace{14mu} {Piece}\mspace{14mu} (g)}{{Area}\mspace{14mu} {of}\mspace{14mu} {Test}\mspace{14mu} {Piece}\mspace{14mu} ( m^{2} )}$

-   -   3. Report the numerical average basis weight for all test        pieces.    -   4. If only a limited amount of non-woven or filter media is        available, basis weight may be measured and reported as the        basis weight of one piece, the largest rectangle possible.

The air filter 50 according to the present invention may be madeaccording to commonly assigned U.S. Pat. Nos. 6,305,046; 6,484,346;6,561,354; 6,645,604; 6,651,290; 6,777,064; 6,790,794; 6,797,357;6,936,330; D409,343; D423,742; D489,537; D498,930; D499,887; D501,609;D511,251 and/or D615,378. The degree of hydrophobicity or hydrophilicityof the fibers may be optimized depending upon the desired goal of theair filter, either in terms of type of particulate or malodor to beremoved, the type of additive that is provided, biodegradability,availability, and combinations of such considerations.

In one embodiment, the air filter 50 is a three layer non-wovencomprising a pre-filter layer, a functional layer and a support layer.In this approach, the pre-filter layer is on the upstream side of theair filter 50 and acts as screen for larger particulates (e.g. greaterthan 10 microns). “Upstream”, as used herein, means a position in an airflow path 90 that is earlier in time from a referenced position, whenmeasuring air flow through an air filtering device. The pre-filter layeris comprised of a high loft structure including hydroentangledpolyester, polypropylene (“PP”), or mixtures thereof. The functionallayer catches smaller particles (e.g. less than about 2.5 microns) andmay serve as the layer comprising any malodor treatment agents. Thefunctional layer may be made from melt-blown or spun-bonded non-woven.The support layer may include high contrast bonded/unbonded areas forvisual indication of the air filter collecting particles. The supportinglayer provides the structure/rigidity desired for the air filter 50. Thesupporting layer may be made from scrim or aperture film.

The type of non-woven and manufacturing method chosen may have a largeimpact on air filter efficiency and on pressure drop and, in turn,pressure needed from the fan 40 to deliver about 50 to about 150 CFM ofair from the device 10. One material with suitable filtering and lowpressure drop is a 60 gsm hydroentangled non-woven comprised ofpolyethylene terephthalate (“PET”) fibers with a 10-20 gsm spunbond PPlayer to provide structure/support for the hydroentangled PET fibers(collectively referred to herein as “60 gsm HET”). With thehydroentangling process, one can achieve a 1 mm to 3 mm thickness withthis construction which enables a lower pressure drop for the same basisweight. Thickness is measured according to the following method thatfollows a modified EDANA 30.5-90 (February 1996) method.

-   -   1. Equipment set-up should include        -   a. Foot Diameter: 40.54 mm (1.596 inch)        -   b. Foot Area: 12.90 cm² (2 in²)        -   c. Foot Weight: 90.72 grams (0.2 lbs)        -   d. Foot Pressure: 7.03 grams/cm² (0.1 psi, 0.69 kPa)        -   e. Dwell time: 10 s    -   2. Measure at least 4 locations, ideally 10. All should be        single layer and without creases. Do not smooth, iron or tension        the material to remove creases. Test pieces need to be larger        than the area of the pressure foot    -   3. Place the uncreased sample under the pressure foot for dwell        time and measure thickness in mm    -   4. Report the numerical average for all test pieces.

It has been found that an air filter density <60 kg/m³ may be desired toprovide meaningful efficiency while also having low pressure drop. Withthe 60 gsm HET material a density from about 20 to about 60 kg/m³ may beprovided. This results in a non-woven that delivers good air filterefficiency and low pressure drop for the device 10 described herein.This is because the fibers are spread out through the thickness enablingmore air flow pathways, resulting in less fiber to fiber contact andmore available fiber surface area to capture particles. Other ways toachieve thickness for a given basis weight include but are not limitedto air bonding, airlaid, needle punching, and carded resin bondedmaterials. The density of the air filter 50 is calculated using thefollowing equation:

${{filter}\mspace{14mu} {density}} = \frac{{basis}\mspace{14mu} {{weight}{\mspace{11mu} \;}( \frac{g}{m^{2}} )}}{{thickness}\mspace{14mu} (m)}$

Another non-woven with good filtering but higher pressure drop is a 59gsm spun bond/melt-blown/spun bond (“SMS”) laminate comprising 10 gsm PPspun bond, bonded to a 34 gsm PP melt-blown, bonded to another 17 gsm PPspunbond non-woven (collectively referred to herein as “59 SMS”). Bothmaterials have a similar basis weight but have very differentthicknesses and densities and, hence, pressure drops. The 60 gsm HETmaterial has a thickness from about 1 mm to about 3 mm, whereas the 59SMS structure has a thickness less than about 1 mm, resulting in adensity greater than 60 kg/m³. The 60 gsm HET material has a lowersingle pass efficiency but also has a pressure drop that is 2 to 3 timeslower enabling a higher air flow rate, lower noise, or less powerrequired for a given fan. The 60 gsm HET material or any material with adensity less than about 60 kg/m³ also has the advantage of being able tohold more dirt/particulates than a more dense filter, such as amelt-blown or SMS material, before it starts to restrict air flow thatagain could impact air flow rate for a fan over the life of the airfilter.

The pore volume distribution of the non-woven characterizes the porosityof the non-woven. It has been found that a non-woven with a preferablepore volume distribution has at least about 15% of the total volume inpores of radii less than about 50 μm, at least about 40% of the totalvolume in pores of radii between about 50 μm to about 100 μm, and atleast about 10% of the total volume in pores of radii greater than about200 μm, where the pore volume distribution is calculated usingmeasurements from the Cumulative Pore Volume Test Method shown below.

Cumulative Pore Volume Test Method

The following test method is conducted on samples that have beenconditioned at a temperature of 23° C.±2.0° C. and a relative humidityof 45%±10% for a minimum of 12 hours prior to the test. All tests areconducted under the same environmental conditions and in suchconditioned room. Discard any damaged product. Do not test samples thathave defects such as wrinkles, tears, holes, and like. All instrumentsare calibrated according to manufacturer's specifications. Samplesconditioned as described herein are considered dry samples (such as “dryfibrous sheet”) for purposes of this invention. At least four samplesare measured for any given material being tested, and the results fromthose four replicates are averaged to give the final reported value.Each of the four replicate samples has dimensions of 55 mm×55 mm Porevolume measurements are made on a TRI/Autoporosimeter (Textile ResearchInstitute (TRI)/Princeton Inc. of Princeton, N.J., U.S.A.). TheTRI/Autoporosimeter is an automated computer-controlled instrument formeasuring pore volume distributions in porous materials (e.g., thevolumes of different size pores within the range from 1 to 1000 μmeffective pore radii). Computer programs such as Automated InstrumentSoftware Releases 2000.1 or 2003.1/2005.1; or Data Treatment SoftwareRelease 2000.1 (available from TRI Princeton Inc.), and spreadsheetprograms are used to capture and analyze the measured data. Moreinformation on the TRI/Autoporosimeter, its operation and datatreatments can be found in the paper: “Liquid Porosimetry: NewMethodology and Applications” by B. Miller and I. Tyomkin published inThe Journal of Colloid and Interface Science (1994), volume 162, pages163-170, incorporated here by reference.

As used in this application, porosimetry involves recording theincrement of liquid that enters or leaves a porous material as thesurrounding air pressure changes. A sample in the test chamber isexposed to precisely controlled changes in air pressure. As the airpressure increases or decreases, different size pore groups drain orabsorb liquid. Pore-size distribution or pore volume distribution canfurther be determined as the distribution of the volume of uptake ofeach pore-size group, as measured by the instrument at the correspondingpressure. The pore volume of each group is equal to this amount ofliquid, as measured by the instrument at the corresponding air pressure.Total cumulative fluid uptake is determined as the total cumulativevolume of fluid absorbed. The effective radius of a pore is related tothe pressure differential by the relationship:

Pressure differential=[(2)γ cos Θ]/effective radius

where γ=liquid surface tension, and Θ=contact angle.

This method uses the above equation to calculate effective pore radiibased on the constants and equipment controlled pressures.

The automated equipment operates by changing the test chamber airpressure in user-specified increments, either by decreasing pressure(increasing pore size) to absorb liquid, or increasing pressure(decreasing pore size) to drain liquid. The liquid volume absorbed ordrained at each pressure increment is the cumulative volume for thegroup of all pores between the preceding pressure setting and thecurrent setting. The TRI/Autoporosimeter reports the pore volumecontribution to the total pore volume of the specimen, and also reportsthe volume and weight at given pressures and effective radii.Pressure-volume curves can be constructed directly from these data andthe curves are also commonly used to describe or characterize the porousmedia.

In this application of the TRI/Autoporosimeter, the liquid is a 0.2weight % solution of octylphenoxy polyethoxy ethanol (Triton X-100 fromUnion Carbide Chemical and Plastics Co. of Danbury, Conn.) in 99.8weight % distilled water (specific gravity of solution is about 1.0).The instrument calculation constants are as follows: ρ (density)=1g/cm³; γ (surface tension)=31 dynes/cm; cos Θ=1. A 1.2 μm MilliporeMixed Cellulose Esters Membrane (Millipore Corporation of Bedford,Mass.; Catalog # RAWP09025) is employed on the test chamber's porousplate. A plexiglass plate weighing about 32 g (supplied with theinstrument) is placed on the sample to ensure the sample rests flat onthe Millipore Filter. No additional weight is placed on the sample.

A blank condition (no sample between plexiglass plate and MilliporeFilter) is run to account for any surface and/or edge effects within thetest chamber. Any pore volume measured for this blank run is subtractedfrom the applicable pore grouping of the test sample. For the testsamples, a 4 cm×4 cm plexiglass plate weighing about 32 g (supplied withthe instrument) is placed on the sample to ensure the sample rests flaton the Millipore filter during measurement. No additional weight isplaced on the sample.

The sequence of pore sizes (pressures) for this application is asfollows (effective pore radius in μm): 10, 20, 30, 40, 50, 60, 70, 80,90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 350, 400,450, 500, 550, 600, 650, 700, 750, 800.

These pressure values are used to produce the Advancing 1 and Receding 1curves. This sequence starts with the sample dry, saturates it as thepressure decreases (i.e., Advancing 1 curve), and then subsequentlydrains the fluid out as the pressure increases again (i.e., Receding 1curve).

The TRI/Autoporosimeter measures the cumulative weight (mg) of liquid ateach pressure level, and reports the respective cumulative pore volumeof the sample. From these data and the weight of the original drysample, the ratio of cumulative pore volume/sample weight can becalculated at any measured pressure level, and reported in mm³/mg. Inthe case of this test method, the cumulative pore volume is determinedduring the Receding 1 curve, and is reported in mm³/mg and taken fromthe TRI instrument.

High thickness and low density at similar basis weights enables a filtermaterial to have good air flow while also still having a lot of fibersurface area to electrostatically attract and/or mechanically filterparticles. This electrostatic benefit can be further enhanced byleveraging PP fibers or other materials/coatings that are negativelychanged in the triboelectric series to help attract positively chargedparticles like hair, skin, and cotton. Optionally, the air filtermaterial can be electrostatically charged via corona treatment at themanufacturing site to help the material maintain a charge for attractingsmall particulates when the fan blows the air through the filtermaterial. Another approach that may deliver improved particle pick-up isionization in the device to help create a charge on the particles in theair such that the particles are attracted to the filter material whenair with particles is passed through the air filter 50 via the fan 40.

The air filter 50 of the present invention may have a total aggregatebasis weight of at least about 30 g/m², alternatively at least about 50g/m², alternatively at least about 70 g/m². The total aggregate basisweight of the present air filter 50 is typically no greater than about200 g/m², alternatively no greater than about 150 g/m², andalternatively no greater than about 100 g/m². The aggregate basis weightcan be measured using the basis weight equation described previously.

The air filter 50 may include air treatment agents to improve theparticulate removal from the air, freshening the air, providinganti-microbial activity, and/or the like. An air freshening agent mayinclude anti-bacterial, anti-viral, or anti-allergen agents; ionic andnon-ionic surfactants; wetting agents; peroxides; ionic and non-ionicpolymers, including those described in US 2012/0183488 and US2012/0183489; metal salts; metal and metal oxides catalysts (e.g. ZPT,Cu, Ag, Zn, ZnO); pH buffering agents; biological agents includingenzymes, natural ingredients and extracts thereof; coloring agents; andperfumes, including those described in U.S. Pub. 2011/0150814, U.S. Pat.No. 8,357,359, U.S. Pub. 2013/0085204. It is also contemplated that theair treatment agent may include vitamins, herbal ingredients, or othertherapeutic or medicinal actives for the nose, throat, and/or lungs.

In some embodiments, the air filter 50 includes conductive materialsand/or carbon particles to help remove odors and/or trap small molecules(VOC's, etc.). The air filter 50 may have high porosity with asubstantially flat surface and open cells or apertures that mayrepresent greater than about 50% of the air filter, or about 50%, orabout 30%, or about 25%, or about 20%, or about 10%. The void volumewithin the air filter 50 may consist of tortuous channels formed withinthe material such as those found in foams, sponges, and filters. Thesurface area may be in the form of tortuous voids within the volume ofthe air filter. The surface area to dimensional area ratio may be aboutgreater than about 2, alternatively greater than about 4.

The air filter 50 may comprise an additive. The type and level ofadditive is selected such that the air filter has the ability toeffectively remove and retain particulate material, while maintainingthe electrostatic properties of the filter and minimizing the amount ofreemission. As such, the additive may be non-cationic, as cationicadditives may tend to diminish the electrostatic properties. In oneembodiment, the air filter 50 is impregnated with a polymeric additive.Suitable polymeric additives include, but are not limited to, thoseselected from the group consisting of pressure sensitive adhesives,tacky polymers, and mixtures thereof. Suitable pressure sensitiveadhesives comprise an adhesive polymer, which is optionally used incombination with a tackifying resin (e.g. Mirapol™ polymer),plasticizer, and/or other optional components. Suitable tacky polymersinclude, but are not limited to, polyisobutylene polymers,N-decylmethacrylate polymers, and mixtures thereof. The adhesivecharacteristics of a polymeric additive may provide effectiveparticulate removal performance. Adhesive characteristics of thepolymeric additives can be measured using a texture analyzer. A suitabletexture analyzer is commercially available from Stable Micro Systems,Ltd. in Godalming, Surrey UK under the trade name TA.XT2 TextureAnalyser.

The air filter 50 of the present invention may have a dirt holdingcapacity of greater than about 1 gram of dirt or about 3 to about 6grams of dirt at an air filter face velocity of 20 to 40 feet/min, whileincreasing pressure drop by less than 12.5 Pa (0.05″ water gauge), orthe increased pressure drop of the additional dirt on filter is lessthan 10 Pa, or less than 5 Pa, or less than 3.5 Pa, or less than 2 Pa.The end-of-life of the air filter 50 may be 30 days, 60 days, 90 or moredays. Dirt holding capacity and change in pressure drop as a result ofadding dirt are measured via a modified ASHRAE 52.1-1992 method.

-   -   1. Measure at least 2 samples of the filter media, 6 or more        preferably as prescribed by the method.    -   2. Measurements are taken on a flat filter sheet, without        pleats, wrinkle, creases, etc, at least 14″×14″. Particles are        then injected across a 1 ft diameter circle of the filter sheet.    -   3. Orient the material in the test apparatus such that particle        hit the same side of the material 1^(st) that will see particles        1^(st) in the device, if the material has different properties        depending on orientation. If the material is non-homogenous        across the area, sample representative materials.    -   4. Run the test with an air filter face velocity chosen to        closely match the air filter face velocity in the device based        on the air filter surface area used in the device and air flow        rate in the device, load to 6 grams of dirt, use ISO Fine A2        dirt (as defined in ISO 12103-1), and load in increments of        0.5 g. Measure resistance after each 0.5 g addition.

The air filter 50 of the present invention has a single pass filteringefficiency of about 20%-70% of E2 particles and about 50-90% of E3particle as defined by modified single pass ASHRAE Standard 52.2 methodbelow. Single pass filtration properties of a filter may be determinedby testing in similar manner to that described in ASHRAE Standard52.2-2012 (“Method of Testing General Ventilation Air-Cleaning Devicesfor Removal Efficiency by Particle Size”). The test involves configuringthe web as a flat sheet (e.g. without pleats, creases or folds)installing the flat sheet into a test duct and subjecting the flat sheetto potassium chloride particles which have been dried andcharge-neutralized. A test face velocity should be chosen to closelymatch the face velocity in the device based on the filter surface areaused in the device and air flow rate in the device. An optical particlecounter may be used to measure the concentration of particles upstreamand downstream from the test filter over a series of twelve particlesize ranges. The equation:

${{Capture}\mspace{14mu} {efficiency}\mspace{14mu} (\%)} = \frac{( {{{upstream}\mspace{14mu} {particle}\mspace{14mu} {count}} - {{downstream}\mspace{14mu} {particle}\mspace{14mu} {count}}} ) \times 100}{( {{upstream}\mspace{14mu} {particle}\mspace{14mu} {count}} )}$

may be used to determine capture efficiency for each particle sizerange. The minimum efficiency for each of the particle size range duringthe test is determined, and the composite minimum efficiency curve isdetermined. From the composite minimum efficiency curve, the fourefficiency values between 0.3 and 1.0 μm may be averaged to provide theE1 Minimum Composite Efficiency (MCE), the four efficiency valuesbetween 1.0 and 3.0 μm may be averaged to provide the E2 MCE, and thefour efficiency values between 3.0 and 10.0 μm may be averaged toprovide the E3 MCE. As a comparison, HEPA filters typically have asingle pass efficiency above 99% for both E2 and E3 particles.

The air filter 50 may take on a variety of configurations. Oneconfiguration for a low cost air filter 50 with high surface area is tofold/seal the air filter material into a shape of a bag instead of atraditional pleated filter with integral frame. An air filter bag can bedesigned such that it is simple to manufacture as well providing acompact form (via folding) for displaying on store shelf in a flow-wrapor resealable pouch.

FIG. 6 shows one possible air filter bag 150 construction and sealpattern with a gusset 66 that is very similar to a typical stand-uppouch with tapered sides, except the gusset 66 is at distal end 60 (i.e.top) versus a typical pouch where the gusset is on bottom, serving as abase to help the bag stand-up and not fall over. Still referring to FIG.6, the air filter bag 150 may be formed by folding and heat-sealing twoor more edges 64 of the air filter 50, creating a bag or tube-like shapewhen inflated with air. The air filter 50 may be sealed in a manner thatcreates a funnel-like shape such that it longitudinally extends from thebase 20 and follows the shape of the outer sleeve 80, but does not touchthe outer sleeve. To reduce the width at the distal end 60 and enablegood air flow between outer sleeve 80 and outer face 62 of the airfilter bag 150, a tapered seal and/or a gusset 66 at the distal end 60may be formed. The air filter bag 150 may include side and/or topgussets that are about 2 cm to about 10 cm, similar to stand-up poucheswhich are formed prior to sealing to help maintain a unique shape wheninflated by fan 40 and help maintain a good spatial gap for air flowbetween the air filter bag 150 and the outer sleeve 60. The air filterbag 150 may have a nominal diameter of about 10 cm to about 40 cm, orabout 10 cm to about 15 cm, or about 20 cm with an upright height ofabout 35 cm to about 50 cm, or about 40 cm, when expanded, to achieve asurface area of about 0.3 m². The heat sealed edges 64 and gusset 66form an air-tight seal, which in some embodiments, withstands more thanabout 40 g/cm peel force to prevent delamination and/or air flow throughunsealed areas.

Outer Sleeve

Still referring to FIGS. 1-3, the device 10 of the present inventionincludes an outer sleeve 80 longitudinally extending from the base 20.The outer sleeve 80 comprises a first open end 82 into which air enters,a second open end 84 from which air exits, and an air flow path 90therebetween. The outer sleeve 80 is releasably attached to the base 20at the first open end 82 and, thus, in air flow communication with theair outlet 24. The outer sleeve 80 envelops the air filter 50 around itslongitudinal axis LA. In this way, the direction of air flow in the airflow path 90 generally aligns with the longitudinal axis LA of the airfilter 50 and outer sleeve 80. While the outer sleeve 80 shown in FIGS.1-3 aligns with the longitudinal axis of the device and air filter, itis contemplated that the second open end 84 of the outer sleeve mayslightly curve away from the longitudinal axis LA, wherein the secondopen is angled about 15 to about 30 degrees from the longitudinal axis.

The outer sleeve 80 may have a diameter at the first open end 82 andsecond open end 84 of about 7 cm to 25 cm, or about 7 cm to about 23 cm,or about 7 cm to about 17 cm, or about 7 cm to about 15 cm. The secondopen 84 end may be smaller than the first open end 82 where the outersleeve 80 is tapered at the second end. The outer sleeve 80 may beelongate—longer along the longitudinal axis LA compared to its depth andwidth. The outer sleeve 80 may be longer along the longitudinal axis LAthan the air filter 50 to assist with capturing air flow through the airfilter. In one embodiment, the outer sleeve 80 may have a length about50 cm along the longitudinal axis LA. The outer sleeve 80 may be about 1cm to about 8 cm longer than air filter 50 to capture air flow exitingthe air filter 50 and directing the air downstream at a velocity thatwill encourage full room circulation.

The outer sleeve 80 may be made of any suitable material that issubstantially impermeable to air. Substantially impermeable, as usedherein, means the volume of air exiting the outer sleeve at the secondopen end 84 is at least about 60% of the air entering the outer sleeveat the first open end 82 when the device is in use (i.e. fan isoperating). In some embodiments, the outer sleeve 80 is air impermeablesuch that the volume of air entering the outer sleeve is equivalent tothe volume of air exiting the outer sleeve. Additionally, in someembodiments, the outer sleeve 80 may be made of a flexible material,such as woven fabrics used in upholstery or outdoor furniture orumbrellas, non-wovens, polyethylene, polyvinyl chloride, acrylic, or thelike, that is capable of collapsing to a generally flat configuration orto less than about 30% of its upright configuration for ease of storageand/or shipment.

It has been learned that there is some advantage of having some lowlevel of permeability of the outer sleeve to provide air dampening. Theouter sleeve has between 10 and 40% of the air passing through the outersleeve to help dampen the sounds from the fan, filter, device system. Inaddition or alternatively the outer sleeve may be made from a soft andflexible or collapsible fabric like material such as felt, outdoorfurniture fabrics, upholstery fabrics, non-wovens and other not rigidmaterials that helps dampen the sound and being somewhat absorbent ofvibrations. This is notably different than most air cleaning systemsthat use rigid injection molded plastics as the housing and means fordirecting air and/or sealing around filter.

Now referring to FIGS. 7 a and 7 b, the outer sleeve 80 may comprise aframe 86 (which includes hinged frames or assembled frames by the userto aid in collapsing for storage) to hold the outer sleeve 80 in anupright configuration. The hinged frame 86 and the flexible material ofthe outer sleeve 80 can be optionally folded or compressed flat orrolled to enable compact design for storage. In other embodiments, theouter sleeve 80 is frameless (i.e. free of a longitudinally extendingframe). In such embodiments, the outer sleeve may be made of a flexiblematerial that includes an integral coil 186 (as shown in FIG. 7B).Alternatively, the outer sleeve may be frameless and made from flexible,spring-like material that enables the outer sleeve to automaticallyexpand into an upright position (i.e. not collapse) when the outersleeve 80 is not compressed into a collapsed configuration by the useror in packaging. Suitable materials that are at least substantiallyimpermeable to air, flexible and spring-like include silicon, elasticfabrics, non-wovens. The material may be 0.25 mm to about 5 mm thick.The collapsibility of the outer sleeve 80 enables the device 10 to bepackaged in a 26 cm×26 cm×15 cm to a 26 cm×41 cm×15 cm outer package.

Optional Features

A control unit (not shown) may be provided in order to operate thedevice 10 and, more specifically, the fan 40. The control unit may bepre-programmed or user-programmed to provide pulsing of current orvoltage to the emitter. In this way, distribution of droplet size anddensity may be controlled over time. The voltage time curves produced bythe power source may also be synchronized with the fan speed and airflow speed so that optimal particulate collection potentials can bemaintained as particulates move through the air filter 50.

Sensors (not shown), chemical or physical in kind, may be used toindicate end-of life of the air filter 50 (i.e. the need for air filterreplacement) and/or monitor the quality of air entering and exitingdevice 10. One approach of providing an end-of-life sensor is with awhite or clear tape that is added to the air filter 50. The tape may bethe same color as the starting color of the air filter 50 such that itis not visible when new but as the air filter accumulates particulatesand becomes dirty, a consumer can visually see a contrast from theaging/dirty filter to the original filter color. Another approach forproviding an end-of-life air filter is to heat-seal the fibers of theair filter 50 with a unique pattern such that there is no air flowthrough the heat-sealed portion of the air filter 50. This heat-sealedportion can be any desired shape and can be colored with ink to matchthe original starting color as needed. Another approach for anend-of-life signal is to provide filter tabs that engage the device tostart a timer that turns on a LED or similar light or sound to remindconsumer to change filter. Another unique approach is to provide a“snooze” button that enables or reminds users to check again after someset desired time (1 week, 1 month, etc. . . . ).

Additionally, a sensor may measure air quality. The air quality sensorcan be used to turn-on the device 10 or increase the fan speed. The airquality sensor can be disposed proximate to the air inlet 22. Thecombination of the air quality sensor at the air inlet 22 and the secondopen end 84 can provide consumers with clear signal of the device'sperformance and demonstrate its efficacy.

A sensor may also be used to determine the device's orientation, haltingits operation if the device 10, for example, is not upright. A sensormay also be used to assess the air flow across device 10 to halt itsoperation if air inlet 22 or air outlet 24 of the is blocked or there isa malfunction of a fan 40.

The device 10 may include a re-usable or disposable fan pre-filter 42housed by a fan pre-filter cover 44. The fan pre-filter 42 may beconstructed from a reticulated foam, a screen, or variety of othermechanical means to keep large particles or other materials fromaccumulating on fan blades or motor. The fan pre-filter 42, when used,is placed upstream of the fan 40 to keep fan blades clean.

Device Performance Exit Velocity

The exit velocity of air leaving the device 10 is also important toprovide good air circulation in a room such that filtering will occur ina larger space. For a medium sized room (approx 80 to 140 ft² with an 8to 9 ft ceiling), an exit velocity greater than about 0.4 meters persecond (“m/s”) is desired to move 1 to 10 micron size air-borneparticles to the device with air flow in the room. For a larger room(approx. 150-225 ft² with an 8 to 9 foot ceiling), an exit velocity ofabout 0.6 m/s or greater is desired. With these velocities the goal isto achieve a room air flow velocity in a significant part of the roomthat is greater than 0.003 m/s to move airborne particles between 1 to10 microns to the device where they can be removed by the filter.

Air flow rates in room that are between about 0.003 m/s and about 0.25m/s are believed good flow rates that will move air-borne particles tothe device while also providing good comfort and not providing draftlike air movement that might be less desirable by room occupants. Thiscan be achieved when the air flow out of the device 10 is from about 50to about 150 CFM with an exit velocity of air exiting the exit orificeor second open end 84 may be from about 0.5 m/s to about 3.0 m/s, orfrom about 0.6 m/s to about 2.6 m/s, or from about 0.7 m/s to about 2.0m/s. While the fan 40 configuration and the RPM of the fan affects CFMof air, other variables impacting CFM of the device 10 include: airfilter surface area, pressure drop of filter media, fan pre-filters,spatial gap between filter and outer sleeve, permeability of outersleeve, and air flow path upstream and downstream of the fan. Thisresults in an air flow rate of the complete device 10 from about 50 toabout 150 CFM, or about 60 to about 100 CFM, or about 70 to about 90CFM. Where the outer sleeve 80 is completely air impermeable and has anair-tight connection to the base 20, the exit velocity of air exitingthe second open end 84 of the outer sleeve 80 can be calculated usingthe below equation:

$\frac{{Air}\mspace{14mu} {flow}\mspace{14mu} {measured}\mspace{14mu} {CFM}\mspace{14mu} {at}\mspace{14mu} {the}\mspace{14mu} {fan}\mspace{14mu} {inlet}}{{Area}\mspace{14mu} {of}\mspace{14mu} {exit}\mspace{14mu} {orifice}\mspace{14mu} {in}\mspace{14mu} ( {ft}^{2} )}$

Table 1 shows exit velocities using the above calculation.

TABLE 1 Exit CFM Diameter Exit Velocity ft3/min inches ft/sec m/sec 50 64.246284501 1.294268 50 8 2.388535032 0.728025 50 10 1.52866242 0.46593675 6 6.369426752 1.941401 75 8 3.582802548 1.092038 75 10 2.2929936310.698904 100 6 8.492569002 2.588535 100 8 4.777070064 1.456051 100 103.057324841 0.931873 150 6 12.7388535 3.882803 150 8 7.1656050962.184076 150 10 4.585987261 1.397809

When the outer sleeve 80 and outer sleeve to base 20 connection iscompletely impermeable, one can use a mass balance with volumetric airflow into fan equal to volumetric flow out thru the exit orifice. Theexit orifice used in calculations for exit velocity should be the areaof the final area of the device as the air is leaving the device (hence,handles in a top ring handle and/or other obstructions should be notused in the area calculation).

Where the outer sleeve 80 is partially permeable to air, the exitvelocity of air exiting the second open end 84 of the outer sleeve canbe calculated using the following equation:

Exiting air flow through second open end of outer sleeve (in CFM)÷areaof exit orifice (in ft²)

To maintain efficient air flow with minimal pressure drop through theair filter 50, the outer sleeve 80 is positioned radially outwardly fromthe air filter 50, forming a spatial gap 100. The spatial gap 100provides a pressure a drop of less than about 8 Pa, or less than about 6Pa, or less than about 4 Pa, or less than about 2 Pa at 80 to 120 CFM ofair. The air filter 50 and the outer sleeve 80 may take on any desiredshape (e.g. cylindrical air filter bag circumferentially surrounded by acylindrical outer sleeve or a squared outer sleeve, etc.). In someembodiments, the spatial gap 100 may be about 3 mm to about 5 mm, or atleast 3 mm, or about 12 mm to about 30 mm, or greater than about 20 mmfrom the air flow surface area of the air filter 50 to the outer sleeve80. The air flow surface area may include a lower region positionedproximal to the attachment member 52 and an upper region distallylocated from the attachment member. Where the fan 40 provides a CFMbetween about 80 to about 100, a suitable minimal spatial gap may be atleast about 3 mm at the lower region and the minimum spatial gap at thedistal upper region may be at least about 15 mm. The spatial gap 100enables more air flow through the air filter 50. If the gap is toosmall, air flow through the air filter may be minimized causing areduction in CFM from the device 10.

Pressure Drop

The pressure drop of the device 10 (the device may include the housing,air filter, outer sleeve, base, grills, fan, fan pre-filter, and anyother components that might limit air flow) is between about 5 and about25 Pa. A device with a HEPA or HEPA-like filter will typically have apressure drop much greater than 25 Pa at flow rates greater than 70 CFM.This higher pressure drop results in higher power consumption, typicallygreater than 25 Watts, in order to deliver greater than 70 CFM with theHEPA or HEPA-like filter. Hence, with the present invention, a fan 40may be selected that will deliver about 50 to about 150 CFM, while underabout 5 to about 25 Pa pressure drop from this device while also keepingthe noise of the total device to be less than about 50 dB(A) per theSound Power measurement described herein, while also operating at a lowpower consumption of less than 25 Watts.

FIG. 10 shows air flow rates of a fan only, a device with fan and airfilter only, and an entire device. From this graph, one can see the airflow with a fan only, without any additional pressure drops from thedevice is about 110 CFM. When the air filter (nominal 2.5-3 ft² lay flatsurface area) is attached to the fan, the air flow drops to about 95CFM. Hence, the air filter is providing a pressure drop of about 7 toabout 8 Pa. This can be more or less depending on the non-woven materialchosen as well as the surface area of the filter bag or any coatings ortreatments of the filter surface. When the air flow of the entire deviceis measured (with the fan activated), a flow rate of about 71 CFM isprovided. Hence, the device provides a total pressure drop of about 14Pa. The volumetric flow rates and pressures of the fan by themselves andin the partial and entire devices can be measured using methods asdescribed in DIN EN ISO 5801:2011-11 The fan curves as shown in FIG. 10can be generated by adjusting the fan static pressure under thedifferent conditions described.

Low Noise

The device 10, when activated (i.e. with the fan operating), may alsoprovide low noise while delivering good air cleaning performance. Theair cleaning performance is driven by the air exit velocity to delivermeaningful full room air circulation, the single pass particle cleaningefficiency of the filter, and the total CFM of the device 10. The noiseof the device 10 can be measured by measuring either sound pressure orsound power. The sound pressure level may be less than about 50 dB(A),or less than about 45 dB(A), or less than about 40 dB(A) with ref. 20uPa. The sound pressure as described herein is measured with a singlemicrophone located 1 m above floor and with 0.2 m horizontal offset fromthe device axis LA. Alternatively, noise can be measured by measuringthe sound power with ref. 1 pW according to a standardized method, e.g.,IEC 60704-2-11. In some embodiments, the device 10 is free of noiseinsulation materials (i.e. any noise insulating parts that are notidentified herein as parts, or optional parts, of the device 10).

Filtering Performance

The device 10 of the present invention may filter greater than 30% orfrom about 40% to about 70% of particulates that are substantially about0.3 microns to about 10 microns in size; in 20 minutes to 40 minutes;with a total pressure drop of the device less than about 75 Pa, or lessthan about 25 Pa, or less than about 20 Pa, or less than about 10 Pa, orless than about 9 Pa; at an air exit velocity from about 0.1 to about4.0 m/s, or from about 0.5 m/s to about 3 m/s, or about 0.8 m/s to about3 m/s, or about 0.8 m/s to about 2.6 m/s, or about 0.6 m/s to about 2.6m/s, or about 0.8 m/s to about 1.8 m/s, or about 0.7 m/s to about 2.0m/s; and an air flow rate greater than about 70 CFM, or from about 70CFM to about 150 CFM. For particles that are greater than 1 micron, thedevice 10 of the present invention can filter greater than 50% ofparticles in 20 minutes; with a pressure drop within the device of lessthan about 25 Pa, or less than about 15 Pa, or less than about 10 Pa; atan exit velocity of about 0.5 m/s to about 3 m/s; and an air flow rategreater than 70 CFM, or from about 70 FM to about 150 CFM. Filteringefficiency of an air filtering device can be determined by using themethod described in ANSI/AHAM-1-2006), as modified in the Examplesherein.

Examples Particulate Removal

A device and air filter in accordance with the present invention wereconstructed for testing particulate removal performance in a room. Thebase was approximately 25 cm×25 cm×3 cm and involved incorporating fourNoctua NF-P12 (120 mm×25 mm) fans into the base with four holes ofapproximately 120 mm diameter to enable air flow such that all fans wereblowing air in same direction (upward from the resting surface). Thefour fans were electrically connected together with the proper spliceand then powered with a 12V DC power supply from a plug-in voltagetransformer (McMaster-Carr part #70235K95). The 25 cm×25 cm×3 cm basealso had four posts mounted on each corner to elevate the device 10 cmoff the floor. On the top of the device, an air filter bag is mountedwith a circumference of approximately 102 cm and elastic means to holdthe air filter bag onto the device.

A second device was made with a higher powered fan to deliver morepressure by replacing the four Noctua fans utilized in the first devicewith a single larger diameter fan (Silverstone S1803212HN, at a diameterof approximately 18 cm) with an opening matching the diameter of theSilverstone fan. This second device also had 10 cm legs to support fanoff the floor without restricting air flow. The Silverstone fan assemblyhad a separate DC power supply that could be varied between 8 and 15volts to change the air flow rate and pressure.

Four different bags were made by folding air filter material andheat-sealing with a Vertrod Impulse bar sealer in the same manner manyplastic bags are made (e.g a potato chip bag). The bags were made withtwo different materials and two different sizes (which affects thefilter face velocity for a given flow rate). One material was a 60 gsmhydroentagled non-woven comprised predominately of PET fibers and a 17gsm spun bond PP non-woven in the middle (“60 gsm HET”). The othermaterial was a 59 gsm laminate consisting of 32 gsm PP melt-blown with a10 gsm spun bond PP on one side and a 17 gsm PP spun bond on the otherside (“59 gsm SMS”).

-   -   1. 60 gsm HET small bag—102 cm circumference×approx. 38 cm        tall—total filter surface area air flow when inflated of        approximately 400 in² due to the tapering of the bag design.    -   2. 60 gsm HET large bag—102 cm circumference×approx. 66 cm        tall—total filter surface area air flow when inflated of 800 in²        due to the tapering of the bag design.    -   3. 59 gsm SMS small bag (used the Silverstone fan due to higher        pressure required)—same size as the 60 gsm HET small bag above.    -   4. 59 gsm SMS large bag (used the Silverstone fan due to higher        pressure required)—same size as the 60 gsm HET large bag above.

The air filter bags are attached to the top of the base which contains aflange to hold the bag and force all the air from the four fans toinflate the bag with all air passing through the filter bag and littleor no by-pass. The air filter bags, when inflated, resemble a tube whereit's attached to the base and the tube then comes to a point where thetop seal is made.

On the outside of the air filter bag is attached an impermeable papersleeve to capture all the air flowing through the air filter bag andforcing it out the top to increase the exit velocity from the device.The outer sleeve is approximately 25 cm×25 cm collapsible paper outersleeve from Ikea (Orgel Vreten™ lamp shade). The outer sleeve isattached to the device such that it is sealed around the base and havingthe filter bag inside. Two different outer sleeve heights are made. Forthe short bags, a 23 cm tall outer sleeve and for the tall bags a 66 cmtall outer sleeve is used. When looking from the top of the assembleddevice one would see the filter bag centered over the device with a 5 mmto 10 mm gap on all sides to enable air flow. The device with the filterbag and outer sleeve are then tested for air flow rate through theentire device by measuring the exit velocity at the top (i.e. secondopen end) of the outer sleeve and then dividing by the air flow surfacearea to get a target flow rate. The desired flow rate for the tests is80 CFM for the small bags and 100 CFM for the tall bags. Table 2captures the test conditions that are reported in FIG. 8.

TABLE 2 Corner TARGET CFM\ Room VOLTAGE, AVG AVG Filter Filter Outer FanAmps, Power Temp Humdity Fans Type Size Sleeve On Req'd PLACEMENT (° C.)(% RH) 1 Noctua HET Small SHORT Yes 80\12 V FLOOR 21.11 36 NF-P12 .5A\5.5 W 2 Noctua HET Small SHORT No 80\12 V FLOOR 21.11 42 NF-P12 .5A\5.4 W 3 Noctua HET Small NONE No 80\12 V FLOOR 21.11 37 NF-P12 .5A\5.4 W 4 Noctua HET Tall TALL Yes 100\12 V FLOOR 21.67 39 NF-P12 .5A\5.3 W 5 SILVER SMS Tall TALL Yes 100\15 V FLOOR 21.67 44 STONE .5A\22.4 W 6 SILVER SMS Small SHORT Yes 80\15 V FLOOR 21.67 37 STONE .5A\24.4 W

The device was then placed in a room that is about 3 m×3 m×3 m similarto that described in ANSI/AHAM AC-1-2006 with Arizona road dust (FineAir Cleaner Test Dust sourced from PTI Inc.). A suitable room andtesting facilities for such testing can be found at Intertek testingfacilities in Cortland, N.Y. A standard concentration of dust (typicallyabout 200-400 particles/cc) was generated in the room as described inSection 6 of the aforementioned ANSI/AHAM method. The device is turnedon per the procedure and the particles from 1 to 10 microns are measuredover a 20 minute time period and plotted as shown in FIG. 8. In additionto the six tests, a natural decay was also recorded to illustrate theparticles natural decay with no air filtering device in the room. Allsix tests and the natural decay test had a similar level of startingparticles in room before the device was turned on but were normalized tocompare all seven variables as a percent reduction. Between each test, aHEPA air cleaner was used to get the particle counts to a very low levelas described in the method.

Using this method and measuring 1 to 10 micron particles, the naturaldecay in 20 minutes for 1 to 10 micron size particles is about 21% withno device running. In contrast, when the device described in thisexample was running, the particles in room are reduced from about 40% toup to 80% depending upon the device, filter, and room set-up conditions.The larger bag enabled higher air flow rate (100 CFM) and higher singlepass efficiency filter (i.e. 59 gsm SMS). The higher efficiency 59 gsmSMS filter required higher voltage with the Silverstone fan. In general,FIG. 8 shows that higher flow rate and higher efficiency both increasefiltering performance. Another plot shown in FIG. 8 shows the impact ofthe outer sleeve when no corner recirculating fan is on. Normally withthe aforementioned ANSI/AHAM method, a high flow rate recirculating fan(greater than 250 CFM/4.25 m³/min) is circulating the air in the roomduring the test. This creates a good mixing of the particles in the roombut is not always representative of what would exist in a home. Hence,the test was conducted with the recirculating corner fan, noted in theANSI/AHAM method, turned off and comparing the benefit with and withoutthe outer sleeve. In this case, there is a 10%+increase in filteringperformance (approx. 50% instead of 40% particle removal for the devicewith a sleeve vs. without a sleeve) since the outer sleeve increases theexit velocity from the device to cause more air flow circulation in theroom and hence remove more particles. With a larger air filter bag andouter sleeve the impact is even greater for a given fan since thedifference between exit velocity and filter face velocity increases. Theparticle reduction in the room due to air circulation of the device willbe impacted as well by how close the particle counter is to the testdevice. If the particle counter is close to the device then the impactof turning off the recirculating fan will be less. If the particlecounter is closer to the corners of the room when the recirculating fanis off, then the impact of the exit velocity (i.e. having outer sleeve)will be higher. The particle counter was about 1.2 m from the airfiltering device being tested. If further placed away, the differencebetween the no-sleeve and presence of a sleeve would be greater sincethe air velocity needed to suspend and move particles towards the deviceis greater.

Effect of Varying Spatial Gaps

Four air filtering devices are constructed: (1) a 23 cm×23 cm×66 cmouter sleeve device having an air filter bag in which about 30% of theair flow surface area is in contact with the outer sleeve; (2) a25×25×66 cm outer sleeve device and (3) a 30×30×66 cm outer sleevedevice both having air filter bags that do not touch the outer sleeve(the latter having a larger spatial gap between the air filter bag andthe inside wall of the outer sleeve than the former); and (4) a devicewithout an outer sleeve. The larger the spatial gap, the lower thepressure drop. Although no outer sleeve is beneficial with respect topressure drop, lacking an outer sleeve has inferior performance incapturing enough air to provide the necessary exit velocities for thedevice to filter air in a room.

The four constructed devices are operated with the same fan—four Noctua12 V fans—providing 80 to 120 CFM of air at 4 to 8 Pa. The air flow andpressure can be calculated by testing the device with the fan using themethods described in DIN EN ISO 5801:2011-11. In the test, the air inletside of the fan or the inlet side of the device (fan, air filter, outersleeve assembly) or the inlet side of the system (fan, filter, sleeveassembly) is attached to the testing rig, blowing the air outwardly fromthe testing rig to a free space.

FIG. 9 shows the relationship between the quantity of air (i.e. CFM) thefan delivers and the pressure generated at various air quantities. CFMis presented along the x-axis. Pressure, the term used to identify the“push” needed to overcome the system's resistance to airflow, ispresented along the y-axis. Typically, for a given fan power, as backpressure increases, flow rate decreases. This curve is constructed byplotting a series of pressure points versus specific flow rates.

FIG. 9 also shows the characteristic of the present four fan device anddifferent air flow resistances. These different air flow resistances aregenerated by different spatial gaps around the air filter. The highestflow rate will be achieved without any additional parts like an outersleeve around the filter. Outside the filter is only free air, but thereis no direction of air flow defined without an outer sleeve. An outersleeve will guide the air flow in a defined direction and will increasethe air flow resistance and, with that, the pressure drops inside thedevice. A smaller spatial gap between outer sleeve and filter increasesthe air velocity but reduces the air flow. It is necessary to optimizethese parameters (air velocity, flow rate, pressure drop) to obtain anair flow which is able to fulfill the requirements in terms of filteringperformance. As seen in FIG. 9, the smallest outer sleeve—23 cm×23 cm×66cm—throttles down the air flow because the spatial gap is nearly zero inmost of gap areas between the outer face of the air filter and theinside surface of the outer sleeve.

Throughout this specification, components referred to in the singularare to be understood as referring to both a single or plural of suchcomponent.

Every numerical range given throughout this specification will includeevery narrower numerical range that falls within such broader numericalrange, as if such narrower numerical range were all expressly writtenherein. Further, the dimensions and values disclosed herein are not tobe understood as being strictly limited to the exact numerical valuesrecited. Instead, unless otherwise specified, each such dimension isintended to mean both the recited value and a functionally equivalentrange surrounding that value. For example, a dimension disclosed as “40mm” is intended to mean “about 40 mm”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An air filtering device comprising: a base havingan air inlet and an air outlet; a fan assembly comprising a fan bladefunctionally attached to said base, wherein said fan assembly moves avolume of air through said air outlet; an air filter bag comprising aplurality of pores for filtering particulates, wherein said air filterbag further comprises a proximal open end in air flow communication withsaid air outlet of said base and a distal closed end, wherein saidproximal open end defines an opening sized to at least circumferencesaid fan blade, and wherein said volume of air flows into said proximalopen end and flows out of said air filter bag through said plurality ofpores; a substantially air impermeable outer sleeve comprising a firstopen end, a second open end, and an air flow path therebetween, whereinsaid outer sleeve is in air flow communication with said air outlet andwherein said outer sleeve is releasably attached to said base at saidfirst open end, and wherein said outer sleeve envelops said air filteraround its longitudinal axis.
 2. The device of claim 1, wherein said fanprovides an air flow of about 50 to about 150 CFM at about 10 Pa toabout 25 Pa of pressure.
 3. The device of claim 1, wherein said fancomprises a diameter of about 10 cm to about 25 cm.
 4. The device ofclaim 1, wherein said air filter bag is releasably attached to saidbase.
 5. The device of claim 1, wherein said air filter bag is taperedat said distal closed end.
 6. The device of claim 4, wherein said airfilter bag comprises an attachment member selected from the groupconsisting of: clips, elastic bands, gripping materials, hook and loopfasteners, and combinations thereof.
 6. The device of claim 1, whereinsaid air filter bag does not contact said outer-sleeve while said deviceis activated.
 7. The device of claim 1, wherein said air filter bag hasan air flow surface area of about 0.1 m² to about 1 m².
 8. The device ofclaim 1, wherein said outer sleeve is air impermeable.
 9. The device ofclaim 1, wherein the air flow exiting said second open end of said outersleeve is at least about 60% of the air flow entering said first end ofsaid outer sleeve.
 10. The device of claim 1, wherein the air flowexiting said second open end of said outer sleeve is at least 80% of theair flow entering said first end of said outer sleeve.
 11. The device ofclaim 1, wherein said outer sleeve is constructed from a flexiblematerial.
 12. The device of claim 1, wherein the exit velocity is about0.5 m/s to about 3.0 m/s.
 13. The device of claim 1, wherein the facevelocity of air exiting said air filter is about 25 to about 50 fpm,when said device is activated.
 14. The device of claim 1, wherein saiddevice provides a pressure drop of less than about 25 Pa.
 15. The deviceof claim 1, wherein said device provides a sound power from about 35dB(a) to about 45 dB(A).
 16. The device of claim 1, wherein said basecomprises a tapered shroud having a first step for receiving said airfilter bag and second step for receiving said first open end of saidouter sleeve.
 17. The device claim 1, further comprising a power sourceproviding less than about 8 Watts of power to activate said fan.
 18. Thedevice of claim 1, further comprising an air quality sensor.
 19. Thedevice of claim 1, further comprising an end-of-life sensor.
 20. An airfiltering device comprising: a base having an air inlet and an airoutlet; a fan functionally attached to said base, wherein said fan movesair through said air outlet when said fan is activated; an air filter inair flow communication with said air outlet, wherein said air filtercomprises a non-woven having a thickness between about 1 and about 3 mm,a density from about 20 kg/m³ to about 60 kg/m³, and a pore volumedistribution of at least about 15% of the total volume is in pores ofradii from about 10 μm to about 50 μm, at least 40% of the total volumeis in pores of radii from about 50 μm and about 100 μm, and at least 10%of the total volume is in pores of radii from about 200 μm to about 800μm; a substantially air impermeable outer sleeve comprising a first openend, a second open end, and an air flow path therebetween, wherein saidouter sleeve is in air flow communication with said air outlet andwherein said outer sleeve is releasably attached to said base at saidfirst open end, and wherein said outer sleeve envelops said air filteraround its longitudinal axis.